                        (map (comp :gross-time :profiling))
                        (apply +))
         net-time (- gross-time kids-time)]
-    (merge tree
-           {:children children
-            :profiling {:gross-time gross-time
-                        :net-time net-time
-                        :kids-time kids-time
-                        :arg-set #{(:args tree)}}})))
+    (assoc tree
+           :children children
+           :profiling {:gross-time gross-time
+                       :net-time net-time
+                       :kids-time kids-time
+                       :arg-set #{(:args tree)}})))
 
 (defn add-metrics-to-rec
   [rec]

                                                         1.0))]
                              (-> metrics
                                  (dissoc :arg-set)
                                  (merge {:gross-time-avg (/ gross-time-sum
                                                             call-count
                                                             1.0)
                                          :net-time-avg  (/ (:net-time-sum metrics)

                                          :arg-cardinality arg-cardinality
                                          :repeat-arg-pct repeat-arg-pct
                                          :gross-of-repeats (* gross-time-sum
                                                               repeat-arg-pct)))))
                          fn-ms))

(defn get-fn-metrics
